MyCustomObject.java

import java.io.IOException;
import java.nio.charset.Charset;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.Collections;

import com.fasterxml.jackson.databind.ObjectMapper;

public class MyCustomObject{
    private String appName;
    public MyCustomObject(String appName){
        this.appName = appName;
    }

    public String getAppName() {
        return appName;
    }

    public static void main(String[] args) throws IOException {
        MyCustomObject app = new MyCustomObject("{\"key\":\"value\"}");
        ObjectMapper mapper = new ObjectMapper();
        String myCustomObjectAsStr = mapper.writeValueAsString(app);

        Files.write(Paths.get("test.json"), Collections.singletonList(myCustomObjectAsStr), Charset.forName("UTF-8"));
    }
}